Radiation excited light source

ABSTRACT

A radiation excited self-luminous light source in which luminescence is provided by the impingement of beta emissions upon a phosphor within the source. A gastight chamber within the source is bounded by a concave phosphor surface and by radiationresistant window. The concave surface is of a predetermined shape designed to maximize the efficiency of the source. In addition, the gastight chamber is designed to withstand pressures of up to 15 atmospheres, thereby enabling gaseous radioisotopes of greater activity to be utilized as the source of beta emissions. In one embodiment, greater efficiency is achieved by utilizing a window having a convex surface which corresponds to the concave phosphor surface and which is positioned a predetermined distance from the phosphor surface equal to the average range of beta emissions within the chamber.

United States Patent Inventors Appl. No.

Filed Patented Assignee Theo F. Linhart, Jr.;

Robert J Doda; Arthur F. Mahon, Tucson, Ariz.

July 19, 1968 Feb. 23, 1971 American Atomics Corporation Tucson, Ariz.

Continuation-impart of application Ser. No. 470,381, July 8, 1965, now abandoned. This application July 19, 1968, Ser. No. 746,145

RADIATION EXCITED LIGHT SOURCE 3,005,102 10/1961 Mac l-lutchin et al. 250/77 3,026,436 3/1962 Hughes 250/71X 3,409,770 11/1968 Clapham, Jr, 250/77X Primary Examiner- Ralph G. Nilson Assistant Examiner-Davis L. Willis Attorney-Christie, Parker and l-lale ABSTRACT: A radiation excited self-luminous light source in which luminescence is provided by the impingement of beta emissions upon a phosphor within the source. A gastight chamber within the source is bounded by a concave phosphor surface and by radiation-resistant window. The concave surface is of a predetermined shape designed to maximize the efficiency of the source. in addition, the gastight chamber is designed to withstand pressures of up to 15 atmospheres, thereby enabling gaseous radioisotopes of greater activity to be utilized as the source of beta emissions. In one embodiment, greater efficiency is achieved by utilizing a window having a convex surface which corresponds to the concave phosphor surface and which is positioned a predetermined distance from the phosphor surface equal to the average range of beta emissions within the chamber.

PATEHTEU FEB23 19m 3566.125

saw 2 0F 3 PATENTEU FEB23 I97! SHEET 3 OF 3 RADEATION EXCITED LIGHT SOURCE CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of application Ser. No. 470,381 filed on Jul. 8, 1965, now abandoned. This invention relates to light sources and, more particularly, to improved self-lurninous light sources of the type which utilizes a phosphor excited by radioactive material.

BRTEF SUMMARY OF THE INVENTION Prior art radiation excited self-luminous sources have utilized phosphor coated surfaces within concavities containing a colorless, beta emitting gas such as Krypton 85 or Tritium. Such prior art sources are disclosed, for example, in US. Pat. Nos. 2,953,684; 3,005,102; and 3,038,271 of J. G. MacHutchin et al. issued on Sept. 20, 1960, Oct. 17, l96l and June 12, i962, respectively. An additional prior art source is disclosed in US. Pat. No. 3,026,436 of .I. D. Hughes, which issued on Mar. 20, 1962, and which discloses a source in which a curved phosphor surface is utilizedin order to make the area of the phosphor coating greater than the area of an aperture through which light is transmitted. The use of a concave phosphor surface as disclosed in the Hughes patent provides an increase in the surface area of the phosphor and an increase in the depth of the cavity, thereby allowing greater amounts of gas (and hence radiation energy) to be included within the cavity and consequently effecting an increase in brightness. The prior art, however, does not disclose the manner in which to determine the dimensions of the curved phosphor surface which will provide an optimum shape for the light source.

Illumination provided by self-luminous radiationexcited light sources results from the impingement of beta emissions upon the phosphor coating within the source. The particular radioactive gas which generated generates the betas will also ordinarily generate gammas which provide an external field and a radiation danger. For a particular light source configuration, the intensity of light produced is directly proportional to the amount of gas used. Such light sources have no bulbs or batteries to replace, no wiring to maintain, no fuel to replenish, and provide long and dependable service, their halflife being from seven to ten years.

Fabrication procedures utilized in prior art self-luminous light sources have often required silver solders or material involving the use of fluxes or acids. The phosphors utilized in such sources must be scrupulously clean at the time of assembling each unit, however, and such fluxes or acids may contaminate the phosphor. Additionally, prior art sources often utilize organic materials which deteriorate under the influence of radiation much more rapidly than do inorganic materials such as metal or radiation-stabilized glass.

An advantage of the present invention is that it provides a radiation-excited self-luminous light source in which a curved phosphor surface of optimum shape is utilized. A shape for this phosphor surface is determined which maximizes the luminous output of the source and minimizes the amount of radioactive gas required for any given diameter of aperture through which the light is transmitted. Thus, the efficiency of the light source is optimized.

Another advantage of the present invention is that no corrosive materials are required during fabrication in order to achieve hermetic seals in self-luminous light sources embodying the present invention.

An additional advantage of the present invention is that is it utilizes inorganic materials such as metal and radiation-stabilized glass, and seals them in a noncorrosive manner so as to provide an airtight chamber which is able to withstand pressures of at least atmospheres.

it is well known that higher pressures of radioactive gas within self-luminous sources produce increases in brightness. The range of the betas emitted by the gas, however, decrease with increases in pressure. Additionally, betas emitted by different radioactive gasses exhibit widely different values of range.

Another advantage of the present inventionis that greater efficiency is achieved by means of utilizing a window having a convex surface which corresponds to the phosphor surface and by positioning the two surfaces a predetermined distance apart dependent upon the range of betas being utilized by the source.

The preceding and other advantages are achieved by means of an improved self-luminous light source in which beta emissions impinge upon a phosphor surface which is concave and which is designed to be of a shape so as to maximize the efficiency of the source. Light generated as a result of the impingement upon the phosphor surface need not pass through a layer of phosphor prior to passing through a glass window and becoming visible to an observer. The entire unit may be fabricated without use of fluxes or corrosive material thereby assuring that the phosphor layer remains scrupulously clean. In addition, the unit is fabricated of inorganic materials such as metal and radiation-stabilized glass and is sealed so as to withstand internalpressures of at least l5 atmospheres.

A light source according to the present invention comprises a core having a concave paraboloidal phosphor surface, a housing within which the core fits and a glass window or envelope covering the core and sealed to the housing. The dimensions for the phosphor surface are determined to provide a light source with optimum efficiency. A copper tube affixed to the housing is used to evacuate the cavity and to in troduce radioactive gas therein, after which it is crimped and sealed. The seals are of a nature to keep the gas filled cavity both moisture free and airtight, and are of sufficient strength to enable pressures of at least 15 atmospheres to be maintained within the cavity. Because of the structural simplicity of light sources embodying the present invention, such seals may be achieved without the use of fluxes or corrosive materials thereby enabling the phosphor to be kept free from contamination during the assembly of the source. Additionally, in one embodiment a glass window having a convex surface which corresponds to the concave phosphor surface is utilized. The two surfaces are positioned a predetermined distance apart and this distance is made substantially equal to the average range of beta emissions within the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS The manner of operation of the present invention and the manner in which it achieves the above and other advantages may be more clearly understood by reference to the following detailed description of the drawings in which:

FIG. 1 depicts a self-luminous light source according to the present invention in which a glass envelope covers a gas filled cavity;

FIG. 2 depicts a self-luminous light source according to the present invention and having a flat discwindow;

FIG. 3 depicts a geometric figure used in determining an optimum shape for the curved phosphor surface within the source;

FIG. 4 depicts a graph also used in determining an optimum shape for the curved phosphor surface within the source;

FIG. 5 depicts graphs illustrating the maximum range of betas emitted by Krypton and Tritium atvarious atmospheric pressures; and

FIG. 6 depicts a self-luminous light source according to the present invention in which a convex window is utilized.

DETAILED DESCRIPTION FIG. 1 depicts a self-luminous light source according to the present invention in which a glass envelope covers a gas filled cavity;

FIG. 2 depicts a self-luminous light source according to the present invention and having a flat disc window;

FIG. 3 depicts a geometric figure used in determining an optimum shape for the curved phosphor surface within the source;

FIG. 4 depicts a graph also used in determining an optimum shape for the curved phosphor surface within the source;

FIG. 5 depicts graphs illustrating the maximum range of betas emitted by Krypton and Tritium at various atmospheric pressures; and

FIG. ti depicts a self-luminous light source according to the present invention in which a convex window is utilized.

DETAILED DESCRIPTION FIG. 1 depicts a self-luminous light source according to the present invention in which a glass envelope covers the gas filled cavity. the core 12 may be metallic. When a metallic core is used, it is preferable to apply a white undercoat to the cavity surface prior to the application of phosphor to the surface. The phosphor is then deposited upon the surface of the cavity in sufficient thickness so that no further increase in light would be obtained by any further increase in coating thickness. in an embodiment using Krypton as the radioisotope, the thickness of this layer will ordinarily be about .06 inch while it will be from .002 to .004 inch if Tritium is used. An inorganic binder such as sodium silicate is used to bind the phosphor to the cavity surface. The phosphor coating is indicated in FlG. l by the line 13. The phosphors used are of the inorganic type such as zinc sulfide and are commercially available from the United States Radium Corporation and other companies. Pigments such as selenides, silicates and others known to respond to beta radiation may be used depending upon the emission required, which may vary from the ultraviolet to the infrared region.

Aluminum is preferable as the metallic core 12 as it will not cause the phosphor to deterioriate or discolor. Also the energy of secondary radiation generated from beta particle impingement on the metal is less for aluminum than for a heavier metal such as stainless steel. It may be advantageous, however, in some cases when internal shielding is desired, to split the core in two portions with the cavitized segment aluminum and the base segment of a high density material such as Mallory metal. The housing 14 may advantageously be made of a metal alloy especially made for the direct fusion of glass to metal. Such alloys are well known. v

The envelope ll is directly fused to housing 14 with no fluxes or corrosive materials being used to effect the joining of housing l4 and envelope ll. A copper tube 15 is brazed to the housing lid with no fluxes or corrosive metals being required to effect the joining of housing M an and tube 15. The tube 15 is utilized to evacuate air from within the chamber formed by core 12 and envelope ill and thereafter to insert a radioactive, beta emitting gas such as Krypton 85, for example, into the chamber.

The air evacuated from the chamber and the radioactive gas introduced into the chamber pass around the core 12 and within envelope ll and housing M, traveling between the chamber and the tube l5. Subsequent to the introduction of radioactive gas into the chamber via tube 15, this tube is crimped and sealed so as to provide a moisture-free and airtight sealed chamber within which the radioactive gas is contained. The tube is sealed at high pressure by means of a metal weld of the tube tip. The sealing of the tube 15 is also accomplished without the use of fluxes or corrosive metal. Copper tubes such as the tube l5 are capable of withstanding pressures of from -to-40 atmospheres. Were the filling tip to be made of glass, however, it is highly unlikely whether the tube tip could be fused with internal pressure of ten atmospheres at standard external barometric pressure. In fact, even at a one atmosphere differential, the problem issevere for a glass tube.

it is well established that higher pressures within the cavity cause a higher brightness output of the source. This results since the fixed volume contains a greater activity of radioactive atoms at higher pressure and hence more radiation particles hit and thereby excite the phosphor to luminescence. it is also established that as pressure is continually increased, the radioactive gas itself begins to absorb more and more of its own radiation energy until at some point further increases in pressure do not cause increases in brightness. lt has been determined experimentally that the brightness increases linearly up to about 10 atmospheres of pressure. Beyond this, the effects of self-absorption start to appear and would be noted by a decrease in slope. At about l5-to-20 atmospheres, a break-even point is reached. By using manufacturing techniques which would allow pressures up to l0-to-l5 atmospheres to be safely and reliably achieved, an increase in brightness output is realized which is from 8-to-l5 times greater than the output realized when from l-to-Z atmospheres of gas are contained within the cavity. Such high pressures, however, cannot be reliably contained in prior art sources which utilize plastic glues or epoxy adhesives. The present invention, however, is designed to safely and reliably achieve pressures of up to 15 atmospheres within the cavity.

As an alternative to the metal core 12, pressed pellet techniques may be utilized to produce the core 12. In this procedure the phosphor is mixed with a small amount of inorganic binder such as sodium silicate pressed in a mold properly designed and fired at an elevated temperature to form an abrasion resistant, luminescent core. Thus, the core itself may be of a luminescent material and a subsequent phosphor deposit is unnecessary. Since a homogenous core of luminescent material is produced, there is no need to form a uniform layer of phosphor material upon the surface of the core. Consequently, in this embodiment, the area 13 represents that portion of the homogeneous core which is actually struck by beta emissions and which produces luminescence in response to being struck. Additionally, the luminescent pellet may be fused'to the glass envelope ll, thereby eliminating core movement within envelope ll whenever this is desirable.

FIG. 2 depicts another embodiment of a self-luminous light source according to the present invention. In this embodiment, a disc-shaped cerium-bearing glass window 21 rather than a glass envelope is used to cover a metallic core 22 having a concave cavity as described previously in connection with FIG. l, and having a phosphor coating indicated by line 23. In an alternative embodiment, the core 22 may also comprise a homogenous luminescent core formed by the pressed pellet technique described above. The core may similarly be fused to the window 21. The core 22 is positioned within the housing 24 which, in turn, is sealed to metallic cap 25. The housing 24 and cap 25 may advantageously be of the same metal alloy as housing 14 of FIG. 1. Housing 24 is fused to window 21. Additionally, housing 243 has a lip which extends over the edge of window 21 and which thereby provides even greater strength. A strength which exceeds the tensile strength of the glass itself may thereby be achieved since the housing 24 provides a compressive stress on the glass at the point of fusion. This compressive stress is obtained by virtue of the metal housing contracting further than the glass window upon cooling after sealing, causing the metal housing to squeeze the glass and thereby provide the compressive stress. The copper tube 26 is again utilized to withdraw air from the chamber within the light source of FIG. 2, and subsequently to introduce radioactive gas such as Krypton or Tritium into this chamber after which it is crimped is crimped and sealed as described in connection with the embodiment of FIG. 1. The tube 26 is sealed to cap 25 in a manner similar to that described in connection with FIG. 1, and a continuous seal is affected all around the flanged connection by the housing 24 and cap 25. All seals are achieved without the use of any fluxes or corrosive metals which might contaminate the phosphor. Additionally, as in FIG. 1, only metallic and inorganic metals are utilized within the unit and pressures of up to 15 atmospheres may easily and as safely be contained within the unit depicted in FIG. 2. Similarly, so dimensions of the curved phosphor surface utilized in the source depicted in FIG. 2 are optimized in the manner described hereinafter.

Additionally, multilayer interference filters 2'7 and 2% may be deposited on the outside and inside, respectively, of glass window 2i. Such interference filters comprise many layers of films having prescribed physical properties, the thickness of each film being at most a few wavelengths of light. Methods have been worked out to achieve controlled reflection of one portion of the spectrum with practically complete rejection of the transmitted light while at other wavelengths nearly 100 percent transmission of the energy is simultaneously achieved. Such interference filters can be designed to have pass bands or to be of a high pass or low pass type. The color of the light produced by the source is controlled by selecting the light frequencies that the filter transmits. Such filters may have transmission band efficiencies in excess of 95 percent while having extremely sharp transitions from reflection to transmission, generally much sharper than has ever been possible with absorption filtering techniques. Such interference filters have in the past been used primarily for laboratory purposes but are now commercially available and may be obtained, for example, from Spectrolab, Inc., North Hollywood, Calif.

FIG. 3 depicts a geometric figure used in determining the of the concave paraboloidal phosphor surface that yield optimum efficiency for light sources. The efficiency is taken to be the ratio of the light output from the source to the volume of radioactive gas used in the source. The optimum is considered isotropic, Le. a radiation particle emitted by an atom has an equal probability of being emitted in any direction. If we take a radioactive atom at any space point located within a volume described by 0 to Y, 0 to X and 9, and on the centerline and if we assume isotropic emission of the atom, then the atom will see a 41rspace, i.e. radiation can be emitted in any direction by the atom. Of this 411 surface that it sees, only a portion is phosphor. This portion is equal to 411-6 where B is the solid angle of space that is not phosphor. Accordingly, the probability of intercepting the phosphor surface for any atom located on the centerline (Y axis) is given by:

To account for atoms not on the Y axis but on any axis parallel to the Y axis and within the 0 to Y, 0 to X and 6 volume of FIG. 1, we use the function f(a). This is simply the projection function on the Y axis of any axis at an angle to the centerline axis. With respect to any space point within the 0 to X, 0 to Y, and 9 volume, the angle ais the angle between the Y axis and the radius vector between the given space point and the origin. The escape probability for a second dimension is given by flu). One minus the product of these two probabilities is to the total interception probability for an a and B dimension. It is given by:

I= l f(a) 8/411. The overall geometric efficiency may be obtained by doubly integrating this total interception probability for 0 to Y and from 0 to X. The overall efficiency for any point within the volume is given by:

f.f w) W 100 This expression for efficiency may be developed by reference to FIG. 3 where for a paraboloid:

The efficiency then becomes:

21r g lv f (a) 100 If we let f(a) equal 1, then the efficiency obtained will be a minimum, i.e., the second term on the right in equation above for efficiency will be a maximum and hence the efficiency will be a minimum. All true efficiencies will be greater than this minimum as the right hand term will be some fraction f(a) of a unit integer value. Both the 9 and a dimensions can be eliminated and the expression for efficiency becomes, on integrating, over the whole volume:

The numerator of this expression for efiiciency represents the area of the phosphor surface, which is proportional to the light output and the denominator represents the volume of the cavity, which is equal to the volume of the gas in the cavity. In the case of a paraboloid, for small dimensions the rate of increase of surface area is greater than the rate of increase of volume, and for large dimensions the rate of increase of volume is greater than the rate of increase of surface area. Between the small dimensions and the large dimensions, there are sets of dimensions, X and Y, at which the ratio of surface area to volume is maximized. One of these sets of dimensions is selected for the phosphor surface.

A graphical solution to the last equation is plotted in FIG. 4. In FIG. 4, graphs of efficiency versus the X dimension are plotted for four different values of the Y dimension. The X dimension represents the radius of the cavity within the light source, while the Y dimension represents the depth of the cavity. FIG. 4 plots the efficiency versus radius for cavities of .100 inch, .200 inch, .300 inch and .400 inch depth, respectively. From the graphs of FIG. 4, it can be noted that for infinite depth of cavity, the efficiency would approach 100 percent for any radius, and that for 0 radius the efficiency would approach 100 percent for any depth. Practical manufacturing considerations, however, dictate that the optimum efficiency be based upon the choosing of X and Y (radius and depth) dimensions within certain constraints. Thus, the volume must be limited to some activity level which is practical. Thus, for example, we may choose an activity level of one-half Curie of a Krypton radioisotope which is achieved by means of 10 atmospheres internal pressure of 4 percent to 5 percent energized Krypton 85 gas. Additionally, a minimum volume is obtained from the design and manufacturing requirements of maintaining dimensions which are large enough to work with. Thus, for example, the phosphor curvature becomes exceedingly difficult to maintain in a mass production basis at less than about l/10-inch radius. These volume limitations result in a range of practical dimensions for optimum efficiency which are depicted in FIG. 4 as falling between a radius of .l to .25 inch.

FIG. 5 depicts graphs showing the maximum range of betas emitted by Krypton 85 and Tritium at various atmospheric pressures, and FIG. 6 depicts an embodiment of the present invention in which a concave window is utilized, and in which the distance between the window and the phosphor surface is made to depend upon the average range of beta emissions within the cavity. It is established that higher pressures of radioactive gas within the cavity will normally produce an increase in brightness. As the pressure is continually increased, however, the radioactive gas itself begins to absorb more and more of its own radiation energy until at some point further increases in pressure do not cause increases in brightness. The range of beta emissions is dependent upon pressure and upon the particular radioisotope emitting the radiation. Thus, the range of Krypton 85 betas is on the order of 5 inches at one atmosphere, while the range of Tritium betas is on the order of .25 inch at 1 atmosphere. At 10 atmospheres pressure the maximum range of Krypton betas is reduced to about .5 inch, while the maximum range for Tritium betas at 10 atmospheres is reduced to about .02 inch.

The efficiency of a radiation-excited light source may be further increased by making the distance between the window and phosphor surface approximately equal to the maximum radiation particle range of the particles within the cavity. FIG. 5 shows the relationship between maximum range and pressure for Krypton betas of average energy and for Tritium betas of average energy. Both Krypton and Tritium have a continuour. spectrum and emit betas which possess a range of energy. For design purposes, however, the relationship between maximum range and beta emissions of average energy for these two radioisotopes may be utilized. The relationship between maximum range and pressures from l-to-lO atmospheres are shown in FIG. for both Tritium and Krypton betas of average energy.

FIG. 6 depicts a self-luminous light source according to the present invention which is identical to the source shown in FIG. 2 except that a cerium-bearing glass window Ml having a convex inner surface is utilized in place of the window 2i having a plain inner surface. The phosphor surface 23 has a shape that produces optimum efficiency as discussed previously with respect to FIGS. 1 and 2. The concave inner surface of window 30 is of a shape corresponding to the shape of the phosphor layer and is maintained a uniform distance away from the phosphor surface. in FIG. 6 this uniform distance away from the phosphor surface. In FIG. 7 this uniform distance is shown as the dimension X. In accordance with the present invention, this dimension X is made substantially equal to the average range of beta emissions within the cavity regardless of the particular radioisotope utilized. This dimension X is a function both of the particular radioisotope used and the pressure within the cavity. As 5 described previously, this relationship is given in FIG. 5 for both Krypton 85 and Tritium.

Two tables in FIG. 6 depict the relationship between dimension X and pressure within the cavity for Tritium and Krypton, respectively. With respect to a light source using Krypton as a radioisotope, the optimum thickness of the phosphor layer would be approximately .060 inch, while for a light source using Tritium as the radioisotope, the optimum thickness of phosphor layer would be approximately .002 to .004 inches. The light source depicted in FIG. 6 achieves improved efficiency both by reason of increasing the likelihood of any given beta emission striking the phosphor surface, and also by reason of the decrease in volume of the cavity as a result of the use of a window having such a convex inner surface. The decreased volume thus requires a smaller amount of radioisotope while the maintenance of a predetermined distance between the window and the phosphor surface maximizes the utilization of the radioisotope within the cavity.

In other words, none of the molecules of radioactive gas within the cavity are a spaced further away from the phosphor surface than the average range of the beta particles. Thus, almost all the beta particles emitted by the radioactive gas reach the phosphor and excite it to luminescence. In contrast, if the cavity were so designed that part of the radioactive gas was much further away from the phosphor surface than the average range of the beta particles, such part of the gas would not contribute appreciable phosphor exciting beta particles and would, therefore, be superfluous.

Self-luminous light sources embodying the present invention lend themselves to many applications where their long life and dependable service together with the elimination of wiring, bulbs, batteries, and fuel to be replenished, and their elimination of maintenance in general, render them particularly useful. Thus, they may be used for signal lanterns or for warning devices which are desired to be independent of a source of power supply. They have many automotive and highway applications such as for permanent parking lights for automobiles, or to define the center or edge of a highway by being permanently set into the highway. They could be set in a road so as to appear green to drivers traveling in one direction and red to drivers traveling in the other direction. They also have many military applications such as for aiming stake lights for artillery field pieces. Such lights have previously required frequent replacement of batteries. They could be built into life jackets or into rafts carried on aircraft for use in ditching at sea, and could be built into such jackets or rafts during manufacture and thereafter require no maintenance. They may be used to outline an aircraft runway and banks of such sources may be utilized to provide items such as runway distance markers. The preceding are intended to be merely illustrative as of some of the many useful applications to which selfJuminous light sources embodying the present invention may be put.

What have been described are considered to be only illustrative embodiments of the present invention. Accordingly, it is to be understood that various and numerous other arrangements may be devised by one skilled in the art without departing from the spirit and scope of this invention.

We claim:

1. A self-luminous light source comprising:

a core having a concave surface of phosphor material;

a housing within which the core fits;

a radiation-resistant window sealed to the housing and covering the concave phosphor surface;

the inside surface of the window being convex as viewed from the concave surface of the core, thereby reducing the volume of the chamber;

the housing and window providing a moisture-free airtight cavity bounded by the phosphor surface and the window; and

a radioactive gas within the chamber, the gas being of a concentration and pressure to excite the phosphor to luminescence.

2. A self-luminous light source according to claim I, in which the concave surface is paraboloidal and the dimensions of the concave surface are. selected so the ratio of the area of the concave surface to the volume of the cavity is maximized.

3. A self-luminous light source according to claim 2, in which the radius of the cavity is within the range of .1 inch to .5 inch.

4. A self-luminous light source according to claim 2 in which a multilayer interference filter is disposed on at least one side of the window.

5. A self-luminous light source according to claim l, in which the radioactive gas emits beta particles that excite the phosphor to luminescence.

6. A self-luminous light source according to claim 1, in which the radioactive gas is Tridium.

7. A self-luminous light source according to claim 1 in which the core, housing, phosphor layer and window comprise radiation-stable inorganic materials and in which the elements are noncorrosively sealed to form the airtight chamber.

8. A self-luminous light source according to claim 7 further comprising a copper filling tube noncorrosively scaled to the housing and welded closed subsequent to the introduction of the radioactive beta emitting gas into the chamber.

9. A self-luminous light source according to claim 8 in which the source is capable of withstanding pressures of up to ten atmospheres within the cavity.

10. A self-luminous light source according to claim 1 in which the convex surface 'of the window matches the concave phosphor surface.

ill. A self-luminous light source according to claim 10, in which the radioactive gas emits beta particles and the convex surface of the window is spaced a predetermined distance from the phosphor surface, this distance being substantially equal to the average range of beta emissions within the cavity.

12. A light source according to claim 1.11 in which Krypton is utilized as the beta emitting gas within the cavity and in which the distance between the window and the phosphor surface bears a relationship to the pressure within the cavity which is substantially in accordance with the graph of range versus pressure for Krypton shown in FIG. 5 herein.

13. A self-luminous light source according to claim 11 in which Tritium is utilized as the beta emitting gas within the cavity and in which the distance between the window and the phosphor surface bears a relationship to the pressure within the cavity which is substantially in accordance with the graph of range versus pressure for Tritium shown in FIG. 5 herein.

M. A self-luminous light source comprising:

a luminescent core having a concave surface;

a housing within which the core fits;

a radiation-resistant window noncorrosively sealed to the housing and covering the concavity the core and window forming a chamber bounded by the concavity and the window;

the inside surface of the window being convex as viewed from the concave surface of the core thereby reducing the volume of the chamber;

means for introducing a radioactive beta emitting gas into the chamber and means for noncorrosively sealing the introduction means subsequent to the introduction of the radioactive gas;

the chamber being made gastight by the noncorrosive seals and being capable of withstanding internal pressures of up to ten atmosphere; and

the gas being of a concentration and pressure to excite the concave portion of the core to luminescence, the luminescent concavity being directly observable through the window.

15. A self-luminous light source according to claim 14 in which the convex surface of the window matches the concave surface of the core.

16. A self-luminous light source according to claim 15 in which the convex surface of the window is spaced a predetermined distance from the concave surface of the core, the distance being substantially equal to the average range of beta emissions within the chamber.

17. A self-luminous light source according to claim 16 in which Krypton is utilized as the beta emitting gas within the chamber and in which the distance between the window and the core bears a relationship to the pressure within the chamber which is substantially in accordance with the graph of range versus pressure for Krypton shown in FIG. herein.

18. A self-luminous light source according to claim 16 in which Tritium is utilized as the beta emitting gas within the chamber and in which the distance between the window and the core bears a relationship to the pressure within the chamber which is substantially in accordance with the graph of range versus pressure for Tritium shown in FIG. 5 herein.

19. A self-luminous light source according to claim 16, in whiclfthe concave surface of the core is paraboloidal and dimensioned to maximize the ratio of the area of the concave surface to the volume of the chamber.

20. A self-luminous light source according to claim 16 in which the core is entirely of a luminescent material.

6 21. A self-luminous light source according to claim 16 in which the luminescent core comprises a metallic core having a layer of phosphor material covering the concave surface thereof.

22. A self-luminous light source comprising:

a supporting structure having a curved surface of phosphorescent material;

means including a window enclosing the supporting structure, the inside surface of the window facing the phosphorescent surface and being curved to match the curve of the phosphorescent surface;

a radioactive gas inside the enclosing means, the gas being of a concentration and pressure to excite the phosphorescent surface to luminescence; and

the inside surface of the window being uniformly spaced a predetermined distance from the phosphorescent surface, the predetermined distance being substantially the average range of the radioactive exciting particles emitted by the gas.

23. The self-luminous light source of claim 22, in which the gas is Tridium.

24. The self-luminous light source of claim 22, in which the phosphorescent surface is concave and the inside surface of the window is convex as viewed from the phosphorescent surface.

25. The self-luminous light source of claim 24, in which the phosphorescent surface is paraboloidal and so dimensioned that the ratio of the area of the phosphorescent surface to the volume inside the enclosing means is maximized.

26. A self-luminous light source comprising:

a supporting structure having a concavely curved surface of phosphorescent material; means including a window enclosing the supporting structure, the inside surface of the window facing the phosphorescent surface and being convexly curved as viewed from the phosphorescent surface, thereby reducing the volume inside the enclosing means; and

a radioactive gas inside the enclosing means, the gas being of a concentration and pressure to excite the phosphorescent surface to luminescence.

27. The self-luminous light source of claim 26, in which the gas is Tridium.

28. The self-luminous light source of claim 26, in which the phosphorescent surface is paraboloidal and so dimensioned that the ratio of the area of the phosphorescent surface to the volume inside the enclosing means is maximized.

29. A self-luminous light source comprising:

a supporting structure having a concave paraboloidal surface of phosphorescent material;

means including a window enclosing the supporting structure, the inside surface of the window facing the phosphorescent surface;

a radioactive gas inside the enclosing means, the gas being of a concentration and pressure to excite the phosphorescent surface to luminescence; and

the phosphorescent surface being so dimensioned that the ratio of the area of the phosphorescent surface to the volume inside the enclosing means is maximized.

30. The self-luminous light source of claim 29, in which the gas is Tridium.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,566 ,125 Dated February 23, 1971 Inventor s Theo F. Linhart, Jr et a1 It is certified that error appears in the above-identified pater and that said Letters Patent are hereby corrected as shown below:

! Column 5, line 17 after "the" insert dimensions I line 21 after "optimum" insert efficiency occurs when t ratio is maximized. Radiation Signed and sealed this 18th day of January 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pa FORM po-roso (IO-69) 

1. A self-luminous light source comprising: a core having a concave surface of phosphor material; a housing within which the core fits; a radiation-resistant window sealed to the housing and covering the concave phosphor surface; the inside surface of the window being convex as viewed from the concave surface of the core, thereby reducing the volume of the chamber; the housing and window providing a moisture-free airtight cavity bounded by the phosphor surface and the window; and a radioactive gas within the chamber, the gas being of a concentration and pressure to excite the phosphor to luminescence.
 2. A self-luminous light source according to claim 1, in which the concave surface is paraboloidal and the dimensions of the concave surface are selected so the ratio of the area of the concave surface to the volume of the cavity is maximized.
 3. A self-luminous light source according to claim 2, in which the radius of the cavity is within the range of .1 inch to .5 inch.
 4. A self-luminous light source according to claim 1 in which a multilayer interference filter is disposed on at least oNe side of the window.
 5. A self-luminous light source according to claim 1, in which the radioactive gas emits beta particles that excite the phosphor to luminescence.
 6. A self-luminous light source according to claim 1, in which the radioactive gas is Tridium.
 7. A self-luminous light source according to claim 1 in which the core, housing, phosphor layer and window comprise radiation-stable inorganic materials and in which the elements are noncorrosively sealed to form the airtight chamber.
 8. A self-luminous light source according to claim 7 further comprising a copper filling tube noncorrosively sealed to the housing and welded closed subsequent to the introduction of the radioactive beta emitting gas into the chamber.
 9. A self-luminous light source according to claim 8 in which the source is capable of withstanding pressures of up to ten atmospheres within the cavity.
 10. A self-luminous light source according to claim 1 in which the convex surface of the window matches the concave phosphor surface.
 11. A self-luminous light source according to claim 10, in which the radioactive gas emits beta particles and the convex surface of the window is spaced a predetermined distance from the phosphor surface, this distance being substantially equal to the average range of beta emissions within the cavity.
 12. A light source according to claim 11 in which Krypton is utilized as the beta emitting gas within the cavity and in which the distance between the window and the phosphor surface bears a relationship to the pressure within the cavity which is substantially in accordance with the graph of range versus pressure for Krypton shown in FIG. 5 herein.
 13. A self-luminous light source according to claim 11 in which Tritium is utilized as the beta emitting gas within the cavity and in which the distance between the window and the phosphor surface bears a relationship to the pressure within the cavity which is substantially in accordance with the graph of range versus pressure for Tritium shown in FIG. 5 herein.
 14. A self-luminous light source comprising: a luminescent core having a concave surface; a housing within which the core fits; a radiation-resistant window noncorrosively sealed to the housing and covering the concavity the core and window forming a chamber bounded by the concavity and the window; the inside surface of the window being convex as viewed from the concave surface of the core thereby reducing the volume of the chamber; means for introducing a radioactive beta emitting gas into the chamber and means for noncorrosively sealing the introduction means subsequent to the introduction of the radioactive gas; the chamber being made gastight by the noncorrosive seals and being capable of withstanding internal pressures of up to ten atmosphere; and the gas being of a concentration and pressure to excite the concave portion of the core to luminescence, the luminescent concavity being directly observable through the window.
 15. A self-luminous light source according to claim 14 in which the convex surface of the window matches the concave surface of the core.
 16. A self-luminous light source according to claim 15 in which the convex surface of the window is spaced a predetermined distance from the concave surface of the core, the distance being substantially equal to the average range of beta emissions within the chamber.
 17. A self-luminous light source according to claim 16 in which Krypton is utilized as the beta emitting gas within the chamber and in which the distance between the window and the core bears a relationship to the pressure within the chamber which is substantially in accordance with the graph of range versus pressure for Krypton shown in FIG. 5 herein.
 18. A self-luminous light source according to claim 16 in which Tritium is utilized as the beta emitting gas within the chamber and in which the distance between the window and the core bears a relationship to the pressure within the chamber which is substantially in accordance with the graph of range versus pressure for Tritium shown in FIG. 5 herein.
 19. A self-luminous light source according to claim 16, in which the concave surface of the core is paraboloidal and dimensioned to maximize the ratio of the area of the concave surface to the volume of the chamber.
 20. A self-luminous light source according to claim 16 in which the core is entirely of a luminescent material. 6
 21. A self-luminous light source according to claim 16 in which the luminescent core comprises a metallic core having a layer of phosphor material covering the concave surface thereof.
 22. A self-luminous light source comprising: a supporting structure having a curved surface of phosphorescent material; means including a window enclosing the supporting structure, the inside surface of the window facing the phosphorescent surface and being curved to match the curve of the phosphorescent surface; a radioactive gas inside the enclosing means, the gas being of a concentration and pressure to excite the phosphorescent surface to luminescence; and the inside surface of the window being uniformly spaced a predetermined distance from the phosphorescent surface, the predetermined distance being substantially the average range of the radioactive exciting particles emitted by the gas.
 23. The self-luminous light source of claim 22, in which the gas is Tridium.
 24. The self-luminous light source of claim 22, in which the phosphorescent surface is concave and the inside surface of the window is convex as viewed from the phosphorescent surface.
 25. The self-luminous light source of claim 24, in which the phosphorescent surface is paraboloidal and so dimensioned that the ratio of the area of the phosphorescent surface to the volume inside the enclosing means is maximized.
 26. A self-luminous light source comprising: a supporting structure having a concavely curved surface of phosphorescent material; means including a window enclosing the supporting structure, the inside surface of the window facing the phosphorescent surface and being convexly curved as viewed from the phosphorescent surface, thereby reducing the volume inside the enclosing means; and a radioactive gas inside the enclosing means, the gas being of a concentration and pressure to excite the phosphorescent surface to luminescence.
 27. The self-luminous light source of claim 26, in which the gas is Tridium.
 28. The self-luminous light source of claim 26, in which the phosphorescent surface is paraboloidal and so dimensioned that the ratio of the area of the phosphorescent surface to the volume inside the enclosing means is maximized.
 29. A self-luminous light source comprising: a supporting structure having a concave paraboloidal surface of phosphorescent material; means including a window enclosing the supporting structure, the inside surface of the window facing the phosphorescent surface; a radioactive gas inside the enclosing means, the gas being of a concentration and pressure to excite the phosphorescent surface to luminescence; and the phosphorescent surface being so dimensioned that the ratio of the area of the phosphorescent surface to the volume inside the enclosing means is maximized.
 30. The self-luminous light source of claim 29, in which the gas is Tridium. 